Accessory Dwelling Unit Plans (Second Dwelling Units)

The Planning and Building Department has created a website to help the public navigate the requirements of ADU projects. You can visit it at Humboldt

In 2007, the Planning and Building Department collaborated with the Humboldt Association of Realtors to make construction plans for 3 different accessory dwelling unit (ADU) designs available to the public. Previously called secondary dwelling units, ADUs are self-contained living units built on the same lot as an existing or proposed primary dwelling. They can be attached, detached, enclosed within an existing building, or built above a garage.

Building codes have changed since 2007 when the plans were drawn. Planning and Building reviewed the plans in October of 2018, and the required changes to meet the 2016 building codes are available here as PDFs. Prior to approving these plans for construction, applicants must make the required modifications to meet California codes in effect at the time the application is submitted.

If the site location is within a State Responsibility Area (SRA) for fire, Section R337 of the building code applies. A PDF of that section is linked below, under Other Application Materials. New construction will also require a Title 24 Energy Report. Information for Title 24 is available at California Energy Commission's Online Resource Center.

For answers to questions about plans, please contact the Building Department at (707) 445-7245

For each Plan, you will find the links below for:

ADU Plan Summary – quick drawing and facts such as type of ADU, square footage, and height;

ADU Plan – full plans for each of three units;

Items Requiring Correction 10.2.18 – Plan reviewer’s determination of corrections to comply with building code as of October 2018; and

Additional Attached Notes for Code Requirements – more detail on required changes.

Plan 1 Documents
Plan 1Detached ADU
Detached ADU Summary (PDF)Detached ADU Items Requiring Correction (PDF)
Detached ADU Plan (PDF)Detached ADU Additional Notes (PDF)
Plan 2 Documents
Plan 2Above Garage ADU
Above Garage ADU Summary (PDF)Above Garage ADU Items Requiring Correction (PDF)
Above Garage ADU Plan (PDF)Above Garage ADU Additional Notes (PDF)
Plan 3 Documents
Plan 3Attached ADU
Attached ADU Summary (PDF)Attached ADU Items Requiring Correction (PDF)
Attached ADU Plan (PDF)Attached ADU Additional Notes (PDF)

Other Application Materials

In addition to making the required modifications on your plans, an application for MS4 Stormwater Erosion and Sediment Control Plan may be required, depending on site location. You will find links to information and application materials for MS4 below, as well as Building Code sections and Calgreen Residential Mandatory Measures referenced in the 2018 Plan Review documents.